This invention relates to an analog-digital converter for converting analog signals into digital signals, and more particularly, to an analog-digital converter in which the threshold level for converting the analog signals, such as image signals, into binary signals is changed in response to changes in the level of the analog signals.
In the field of pattern recognition, image signals from an image pick-up device, such as an industrial TV camera, are converted into binary signals based on a constant threshold level.
In this case, no binary signals with long-term stability have been obtained since the gains and the DC levels of the image signals vary at relatively slow speeds due to variations in temperature and brightness under various conditions.